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# A Provider is an implementation of the actions that manage resources (of some type) on a system.
# This class is the base class for all implementation of a Puppet Provider.
# Concepts:
# * **Confinement** - confinement restricts providers to only be applicable under certain conditions.
# It is possible to confine a provider several different ways:
# * the included {#confine} method which provides filtering on fact, feature, existence of files, or a free form
# predicate.
# * the {commands} method that filters on the availability of given system commands.
# * **Property hash** - the important instance variable `@property_hash` contains all current state values
# for properties (it is lazily built). It is important that these values are managed appropriately in the
# methods {instances}, {prefetch}, and in methods that alters the current state (those that change the
# lifecycle (creates, destroys), or alters some value reflected backed by a property).
# * **Flush** - is a hook that is called once per resource when everything has been applied. The intent is
# that an implementation may defer modification of the current state typically done in property setters
# and instead record information that allows flush to perform the changes more efficiently.
# * **Execution Methods** - The execution methods provides access to execution of arbitrary commands.
# As a convenience execution methods are available on both the instance and the class of a provider since a
# lot of provider logic switch between these contexts fairly freely.
# * **System Entity/Resource** - this documentation uses the term "system entity" for system resources to make
# it clear if talking about a resource on the system being managed (e.g. a file in the file system)
# or about a description of such a resource (e.g. a Puppet Resource).
# * **Resource Type** - this is an instance of Type that describes a classification of instances of Resource (e.g.
# the `File` resource type describes all instances of `file` resources).
# (The term is used to contrast with "type" in general, and specifically to contrast with the implementation
# class of Resource or a specific Type).
# @note An instance of a Provider is associated with one resource.
# @note Class level methods are only called once to configure the provider (when the type is created), and not
# for each resource the provider is operating on.
# The instance methods are however called for each resource.
# @api public
class Puppet::Provider
include Puppet::Util
include Puppet::Util::Errors
include Puppet::Util::Warnings
extend Puppet::Util::Warnings
require 'puppet/confiner'
require 'puppet/provider/command'
extend Puppet::Confiner
Puppet::Util.logmethods(self, true)
class << self
# Include the util module so we have access to things like 'which'
include Puppet::Util, Puppet::Util::Docs
include Puppet::Util::Logging
# @return [String] The name of the provider
attr_accessor :name
# @todo Original = _"The source parameter exists so that providers using the same
# source can specify this, so reading doesn't attempt to read the
# same package multiple times."_ This seems to be a package type specific attribute. Is this really
# used?
# @return [???] The source is WHAT?
attr_writer :source
# @todo What is this type? A reference to a Puppet::Type ?
# @return [Puppet::Type] the resource type (that this provider is ... WHAT?)
attr_accessor :resource_type
# @!attribute [r] doc
# The (full) documentation for this provider class. The documentation for the provider class itself
# should be set with the DSL method {desc=}. Setting the documentation with with {doc=} has the same effect
# as setting it with {desc=} (only the class documentation part is set). In essence this means that
# there is no getter for the class documentation part (since the getter returns the full
# documentation when there are additional contributors).
# @return [String] Returns the full documentation for the provider.
# @see Puppet::Utils::Docs
# @comment This is puzzling ... a write only doc attribute??? The generated setter never seems to be
# used, instead the instance variable @doc is set in the `desc` method. This seems wrong. It is instead
# documented as a read only attribute (to get the full documentation). Also see doc below for
# desc.
# @!attribute [w] desc
# Sets the documentation of this provider class. (The full documentation is read via the
# {doc} attribute).
# @dsl type
attr_writer :doc
# @return [???] This resource is what? Is an instance of a provider attached to one particular Puppet::Resource?
attr_accessor :resource
# Convenience methods - see class method with the same name.
# @see execute
# @return (see execute)
def execute(*args)
# (see Puppet::Util::Execution.execute)
def self.execute(*args)
# Convenience methods - see class method with the same name.
# @see execpipe
# @return (see execpipe)
def execpipe(*args, &block)
Puppet::Util::Execution.execpipe(*args, &block)
# (see Puppet::Util::Execution.execpipe)
def self.execpipe(*args, &block)
Puppet::Util::Execution.execpipe(*args, &block)
# Convenience methods - see class method with the same name.
# @see execfail
# @return (see execfail)
def execfail(*args)
# (see Puppet::Util::Execution.execfail)
def self.execfail(*args)
# Returns the absolute path to the executable for the command referenced by the given name.
# @raise [Puppet::DevError] if the name does not reference an existing command.
# @return [String] the absolute path to the found executable for the command
# @see which
# @api public
def self.command(name)
name = name.intern
if defined?(@commands) and command = @commands[name]
# nothing
elsif superclass.respond_to? :command and command = superclass.command(name)
# nothing
raise Puppet::DevError, "No command #{name} defined for provider #{}"
# Confines this provider to be suitable only on hosts where the given commands are present.
# Also see {Puppet::Confiner#confine} for other types of confinement of a provider by use of other types of
# predicates.
# @note It is preferred if the commands are not entered with absolute paths as this allows puppet
# to search for them using the PATH variable.
# @param command_specs [Hash{String => String}] Map of name to command that the provider will
# be executing on the system. Each command is specified with a name and the path of the executable.
# @return [void]
# @see optional_commands
# @api public
def self.commands(command_specs)
command_specs.each do |name, path|
has_command(name, path)
# Defines optional commands.
# Since Puppet 2.7.8 this is typically not needed as evaluation of provider suitability
# is lazy (when a resource is evaluated) and the absence of commands
# that will be present after other resources have been applied no longer needs to be specified as
# optional.
# @param [Hash{String => String}] hash Named commands that the provider will
# be executing on the system. Each command is specified with a name and the path of the executable.
# (@see #has_command)
# @see commands
# @api public
def self.optional_commands(hash)
hash.each do |name, target|
has_command(name, target) do
# Creates a convenience method for invocation of a command.
# This generates a Provider method that allows easy execution of the command. The generated
# method may take arguments that will be passed through to the executable as the command line arguments
# when it is invoked.
# @example Use it like this:
# has_command(:echo, "/bin/echo")
# def some_method
# echo("arg 1", "arg 2")
# end
# @comment the . . . below is intentional to avoid the three dots to become an illegible ellipsis char.
# @example . . . or like this
# has_command(:echo, "/bin/echo") do
# is_optional
# environment :HOME => "/var/tmp", :PWD => "/tmp"
# end
# @param name [Symbol] The name of the command (will become the name of the generated method that executes the command)
# @param path [String] The path to the executable for the command
# @yield [ ] A block that configures the command (see {Puppet::Provider::Command})
# @comment a yield [ ] produces {|| ...} in the signature, do not remove the space.
# @note the name ´has_command´ looks odd in an API context, but makes more sense when seen in the internal
# DSL context where a Provider is declaratively defined.
# @api public
def self.has_command(name, path, &block)
name = name.intern
command = CommandDefiner.define(name, path, self, &block)
@commands[name] = command.executable
# Now define the class and instance methods.
create_class_and_instance_method(name) do |*args|
return command.execute(*args)
# Internal helper class when creating commands - undocumented.
# @api private
class CommandDefiner
private_class_method :new
def self.define(name, path, confiner, &block)
definer = new(name, path, confiner)
definer.instance_eval(&block) if block
def initialize(name, path, confiner)
@name = name
@path = path
@optional = false
@confiner = confiner
@custom_environment = {}
def is_optional
@optional = true
def environment(env)
@custom_environment = @custom_environment.merge(env)
def command
if not @optional
@confiner.confine :exists => @path, :for_binary => true
end, @path, Puppet::Util, Puppet::Util::Execution, { :failonfail => true, :combine => true, :custom_environment => @custom_environment })
# @return [Boolean] Return whether the given feature has been declared or not.
def self.declared_feature?(name)
defined?(@declared_features) and @declared_features.include?(name)
# @return [Boolean] Returns whether this implementation satisfies all of the default requirements or not.
# Returns false if there is no matching defaultfor
# @see Provider.defaultfor
def self.default?
default_match ? true : false
# Look through the array of defaultfor hashes and return the first match.
# @return [Hash<{String => Object}>] the matching hash specified by a defaultfor
# @see Provider.defaultfor
# @api private
def self.default_match
@defaults.find do |default|
default.all? do |key, values|
case key
when :feature
fact_match(key, values)
def self.fact_match(fact, values)
values = [values] unless values.is_a? Array! { |v| v.to_s.downcase.intern }
if fval = Facter.value(fact).to_s and fval != ""
fval = fval.to_s.downcase.intern
def self.feature_match(value)
Puppet.features.send(value.to_s + "?")
# Sets a facts filter that determine which of several suitable providers should be picked by default.
# This selection only kicks in if there is more than one suitable provider.
# To filter on multiple facts the given hash may contain more than one fact name/value entry.
# The filter picks the provider if all the fact/value entries match the current set of facts. (In case
# there are still more than one provider after this filtering, the first found is picked).
# @param hash [Hash<{String => Object}>] hash of fact name to fact value.
# @return [void]
def self.defaultfor(hash)
@defaults << hash
# @return [Integer] Returns a numeric specificity for this provider based on how many requirements it has
# and number of _ancestors_. The higher the number the more specific the provider.
# The number of requirements is based on the hash size of the matching {Provider.defaultfor}.
# The _ancestors_ is the Ruby Module::ancestors method and the number of classes returned is used
# to boost the score. The intent is that if two providers are equal, but one is more "derived" than the other
# (i.e. includes more classes), it should win because it is more specific).
# @note Because of how this value is
# calculated there could be surprising side effects if a provider included an excessive amount of classes.
def self.specificity
# This strange piece of logic attempts to figure out how many parent providers there
# are to increase the score. What is will actually do is count all classes that Ruby Module::ancestors
# returns (which can be other classes than those the parent chain) - in a way, an odd measure of the
# complexity of a provider).
match = default_match
length = match ? match.length : 0
(length * 100) + { |a| a.is_a? Class }.length
# Initializes defaults and commands (i.e. clears them).
# @return [void]
def self.initvars
@defaults = []
@commands = {}
# Returns a list of system resources (entities) this provider may/can manage.
# This is a query mechanism that lists entities that the provider may manage on a given system. It is
# is directly used in query services, but is also the foundation for other services; prefetching, and
# purging.
# As an example, a package provider lists all installed packages. (In contrast, the File provider does
# not list all files on the file-system as that would make execution incredibly slow). An implementation
# of this method should be made if it is possible to quickly (with a single system call) provide all
# instances.
# An implementation of this method should only cache the values of properties
# if they are discovered as part of the process for finding existing resources.
# Resource properties that require additional commands (than those used to determine existence/identity)
# should be implemented in their respective getter method. (This is important from a performance perspective;
# it may be expensive to compute, as well as wasteful as all discovered resources may perhaps not be managed).
# An implementation may return an empty list (naturally with the effect that it is not possible to query
# for manageable entities).
# By implementing this method, it is possible to use the `resources´ resource type to specify purging
# of all non managed entities.
# @note The returned instances are instance of some subclass of Provider, not resources.
# @return [Array<Puppet::Provider>] a list of providers referencing the system entities
# @abstract this method must be implemented by a subclass and this super method should never be called as it raises an exception.
# @raise [Puppet::DevError] Error indicating that the method should have been implemented by subclass.
# @see prefetch
def self.instances
raise Puppet::DevError, "Provider #{} has not defined the 'instances' class method"
# Creates getter- and setter- methods for each property supported by the resource type.
# Call this method to generate simple accessors for all properties supported by the
# resource type. These simple accessors lookup and sets values in the property hash.
# The generated methods may be overridden by more advanced implementations if something
# else than a straight forward getter/setter pair of methods is required.
# (i.e. define such overriding methods after this method has been called)
# An implementor of a provider that makes use of `prefetch` and `flush` can use this method since it uses
# the internal `@property_hash` variable to store values. An implementation would then update the system
# state on a call to `flush` based on the current values in the `@property_hash`.
# @return [void]
def self.mk_resource_methods
[resource_type.validproperties, resource_type.parameters].flatten.each do |attr|
attr = attr.intern
next if attr == :name
define_method(attr) do
if @property_hash[attr].nil?
define_method(attr.to_s + "=") do |val|
@property_hash[attr] = val
# This method is used to generate a method for a command.
# @return [void]
# @api private
def self.create_class_and_instance_method(name, &block)
unless singleton_class.method_defined?(name)
meta_def(name, &block)
unless method_defined?(name)
define_method(name) do |*args|
self.class.send(name, *args)
private_class_method :create_class_and_instance_method
# @return [String] Returns the data source, which is the provider name if no other source has been set.
# @todo Unclear what "the source" is used for?
def self.source
@source ||=
# Returns true if the given attribute/parameter is supported by the provider.
# The check is made that the parameter is a valid parameter for the resource type, and then
# if all its required features (if any) are supported by the provider.
# @param param [Class, Puppet::Parameter] the parameter class, or a parameter instance
# @return [Boolean] Returns whether this provider supports the given parameter or not.
# @raise [Puppet::DevError] if the given parameter is not valid for the resource type
def self.supports_parameter?(param)
if param.is_a?(Class)
klass = param
unless klass = resource_type.attrclass(param)
raise Puppet::DevError, "'#{param}' is not a valid parameter for #{}"
return true unless features = klass.required_features
dochook(:defaults) do
if @defaults.length > 0
return @defaults.collect do |d|
"Default for " + d.collect do |f, v|
"`#{f}` == `#{[v].flatten.join(', ')}`"
end.sort.join(" and ") + "."
end.join(" ")
dochook(:commands) do
if @commands.length > 0
return "Required binaries: " + @commands.collect do |n, c|
end.sort.join(", ") + "."
dochook(:features) do
if features.length > 0
return "Supported features: " + features.collect do |f|
end.sort.join(", ") + "."
# Clears this provider instance to allow GC to clean up.
def clear
@resource = nil
# (see command)
def command(name)
# Returns the value of a parameter value, or `:absent` if it is not defined.
# @param param [Puppet::Parameter] the parameter to obtain the value of
# @return [Object] the value of the parameter or `:absent` if not defined.
def get(param)
@property_hash[param.intern] || :absent
# Creates a new provider that is optionally initialized from a resource or a hash of properties.
# If no argument is specified, a new non specific provider is initialized. If a resource is given
# it is remembered for further operations. If a hash is used it becomes the internal `@property_hash`
# structure of the provider - this hash holds the current state property values of system entities
# as they are being discovered by querying or other operations (typically getters).
# @todo The use of a hash as a parameter needs a better exaplanation; why is this done? What is the intent?
# @param resource [Puppet::Resource, Hash] optional resource or hash
def initialize(resource = nil)
if resource.is_a?(Hash)
# We don't use a duplicate here, because some providers (ParsedFile, at least)
# use the hash here for later events.
@property_hash = resource
elsif resource
@resource = resource
@property_hash = {}
@property_hash = {}
# Returns the name of the resource this provider is operating on.
# @return [String] the name of the resource instance (e.g. the file path of a File).
# @raise [Puppet::DevError] if no resource is set, or no name defined.
def name
if n = @property_hash[:name]
return n
elsif self.resource
raise Puppet::DevError, "No resource and no name in property hash in #{} instance"
# Sets the given parameters values as the current values for those parameters.
# Other parameters are unchanged.
# @param [Array<Puppet::Parameter>] params the parameters with values that should be set
# @return [void]
def set(params)
params.each do |param, value|
@property_hash[param.intern] = value
# @return [String] Returns a human readable string with information about the resource and the provider.
def to_s
# @return [String] Returns a human readable string with information about the resource and the provider.
def inspect
# Makes providers comparable.
include Comparable
# Compares this provider against another provider.
# Comparison is only possible with another provider (no other class).
# The ordering is based on the class name of the two providers.
# @return [-1,0,+1, nil] A comparison result -1, 0, +1 if this is before other, equal or after other. Returns
# nil oif not comparable to other.
# @see Comparable
def <=>(other)
# We can only have ordering against other providers.
return nil unless other.is_a? Puppet::Provider
# Otherwise, order by the providers class name.
return <=>
# @comment Document prefetch here as it does not exist anywhere else (called from transaction if implemented)
# @!method self.prefetch(resource_hash)
# @abstract A subclass may implement this - it is not implemented in the Provider class
# This method may be implemented by a provider in order to pre-fetch resource properties.
# If implemented it should set the provider instance of the managed resources to a provider with the
# fetched state (i.e. what is returned from the {instances} method).
# @param resources_hash [Hash<{String => Puppet::Resource}>] map from name to resource of resources to prefetch
# @return [void]
# @api public
# @comment Document post_resource_eval here as it does not exist anywhere else (called from transaction if implemented)
# @!method self.post_resource_eval()
# @since 3.4.0
# @api public
# @abstract A subclass may implement this - it is not implemented in the Provider class
# This method may be implemented by a provider in order to perform any
# cleanup actions needed. It will be called at the end of the transaction if
# any resources in the catalog make use of the provider, regardless of
# whether the resources are changed or not and even if resource failures occur.
# @return [void]
# @comment Document flush here as it does not exist anywhere (called from transaction if implemented)
# @!method flush()
# @abstract A subclass may implement this - it is not implemented in the Provider class
# This method may be implemented by a provider in order to flush properties that has not been individually
# applied to the managed entity's current state.
# @return [void]
# @api public
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